Method of making a composite metal structure



I F: [WWW METHOD OF MAKING A COMPOSITE METAL STRUCTURE Filed Dec. 30,1937 OOOOOOOO wvwO a 0N mm Mm v T P m m 5V IBM 0 H ratented Feb. 13,1940 FATE OFl

METHOD OF MAKING A COMPOSITE METAL STRUCTURE Application December 30,1937, Serial No. 182,411

7 Claims.

The present invention relates to metallic structures and moreparticularly to a method of fabricating porous metal structures thathave a metallic ingredient dispersed within the interstitial poresthereof.

It is an object of the present invention to provide a method offabricating a porous alloy structure from a porous metal matrix whichcomprises, impregnating a previously fiuxed porous metal matrix with ametal at such a temperature and for such a time as to prevent theimpregnating metal from dissolving the porous metal matrix, and thensubsequently heating the impregnated matrix and thereby causing at leasta part of the impregnating metal to substantially uniformly diffuse intothe metal of the matrix and form an alloy therewith without destroyingthe continuity of the porous metal matrix.

It is a further object, in some cases, to im- 2 0 pregnate the porousmetal matrix with a mixture of two metals, one of which is readilyalloyable with the metal of the matrix and the other of which is notreadily alloyable with the metal of the matrix, the impregnated matrixbeing subsequently heated to cause the readily alloyable metal touniformly diffuse intothe metal of the matrix and alloy therewithwithout destroying the continuity of the matrix and leave the lessreadily alloyab-le metal dispersed within the pores of the matrix.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawing wherein a preferred embodiment of the present invention isclearly shown.

In the drawing:

The single figure is a diagrammatic view, illustrating a method ofapplying loose uncompacted metal powder in a layer upon a strong metalback and sintering the loose layer in situ upon the metal back to form aporous metal matrix directly bonded to th bank by an alloy bond.

The present invention is directed to a low temperattu'e impregnatingmethod whereby readily alloyable metals may be impregnated into a metalmatrix or sponge at low temperatures and subsequently the impregnatedsponge may be heated to cause uniform alloying of all or a part of thealloyable impregnating metal with the sponge without any harmfuleffects, such as destroying the continuity of the sponge.

In practicing such a method it is possible to substantially uniformlyimpregnate a copper sponge with pure tin and later heat the impregnatedsponge and thereby cause the tin substantially uniformly diffuse intothe copp of the matrix and alloy therewith to form bronze sponge insitu, having substantially tl same continuous structure as the originalcopp sponge. Likewise, a pure copper sponge may I impregnated with amixtureeof -lead and ti: The impregnated sponge may be subsequent heatedto cause the tin to uniformly dissolve int the copper to form an alloytherewith leavir the less alloyable lead uniformly dispersed withi thepores of the newly formed bronze sponge.

The present method can be advantageous carried out with any number ofmetallic sponge for example, copper, iron, nickel,,bronze spongecopper-nickel sponges. etc..,. together wit sponges which include anon-metallic disperse material therein, such -as'graphite. Imp'i'egnaiing metals such as tin, silver, aluminum, bismutl bismuth-lead alloys,tin-lead alloys, tin-silve alloys and many other metals and alloysthere( can all be used to advantage.

While the following .description is directed t impregnating andsubsequently alloying or par tially alloying the impregnated metal withsponge or matrix which is directly bonded to steel back, it should beunderstood that the meth od is not limited in this respect and may beuse with equal success on sponges that have no sup porting backs.

Referring to the drawing a loose layer H] c the desired thickness of thefinely divided matrix forming metal powder is applied onto a relativelstrong metal strip H, such as steel, as the stri l l moves along underthe hopper I2 at a suitabl; slow uniform speed. The loose matrix-forminmetal powder I3 in hopper l2 runs out by th aid of gravity upon strip IIand is preferabl; smoothed thereon by a suitable adjustabl smoothingdevice I4 to provide a smooth-sur faced uniform layer H] of loose metalpowde upon the strip I I.

The moving metal strip H with the loose laye ill thereon passes into thesintering chamber 2 and is there heated in a non-oxidizing or reduc ingatmosphere to such a temperature and f0 such a time as will cause theloose or only slight]; compacted metal particles to molecularly 1001together and form a strong highly porous matri: lining l5 and at thesame time to molecularl: bond to the metal strip I I. During thissintering process the thickness of the loose powder laye: I0 ismaterially reduced due to shrinkage s that the porous metal lining l5emerging at 2 from the sintering chamber 20 is about one d less than theloose powder layer II) which :rs chamber 20. Hence, the original thickofthe powder layer I is made such as will the desired thickness anddensity of the sind porous metal matrix lining ID. This can eadilydetermined by trial for any given inlients in the matrix-forming metalpowder l3. trip H is of steel it is preferably, but not zssarily, firstcopper plated before the loose 'der layer I0 is applied thereon since ithas 1 found that the sintered porous lining l5 will d somewhat morestrongly to a copper surface a it will to a steel surface. However, the)us matrix lining l5 will bond successfully to uncoated clean steelsurface. The temperaof the sintering chamber is accurately conled bysuitable means and is preferably heaty electric heating elements 25. behighly porous matrix lining [5 preferably ;es from the sintering chamber20 into the er jacketed cooling chamber 22 where it is ed undernon-oxidizing or reducing condis to substantially prevent oxidation ofthe )us metal matrix. The reducing or nonlizing gas is admitted to thesintering chamber hrough an inlet 23 and then escapes through outlet 24of the cooling chamber 22. In manner the non-oxidizing atmosphere is;ent in both chambers 20 and 22 and at a ;sure slightly in excess ofatmospheric presa to assure that no atmospheric gases enteraforementioned chambers. 'he density or porosity of porous matrix lining:an be accurately controlled, if desired, by subiently sizing the liningby a pressure opera- 1, for example, by passing strip II with the ouslining l5 bonded thereto between pressure 5 30 and 3| illustrated in thedrawing. These s 30 and 3| may be set any desired distance .rt so as tocompress the lining l5 to any ired thickness, thereby reducing theporosity reof. .fter the porous metal lining I5 has been lded to stripII the lined strip is preferably into short lengths which may then beimrsed in a fluxing bath either under vacuum inder atmosphericconditions, or the strip may painted with the fluxing material, such asamnium or zinc chloride, rosin and alcohol, borax ition etc., or exposedto an atmosphere of a (ing gas. The fluxed strip is then immersed amolten bath of the desired impregnating tal. It is preferable to utilizea vacuum durimpregnation to draw the occluded air and Les from the poresof the matrix prior to imrsing the same in the impregnating metal bath 1then apply pressure to the bath by increasthe pressure thereover toforce the impreg- ;ing metal into the pores of the immersed metal vnge.The impregnated metal sponge is then moved from the impregnating bathand pref- ,bly cooled, although the cooling step is not :essary to thesuccess of the steps that follow. bsequently the sponge may be heatedunder o-oxidizing or reducing conditions to a temrature well above theimpregnating temperae, to cause the impregnated metal to alloy orrtially alloy with the metal of the matrix. In trying out theaforementioned steps it has an discovered that the fluxing step may beminated if the sintered metal matrix is imagnated before exposure toatmospheric air ice the surfaces therein are substantially free moxidation or other surface films. A. specific example of the fabricationof a copper sponge impregnated with tin by such procedure is as follows:Uncompacted copper powder on a steel strip is preferably sintered at atemperature of approximately 1900" F. for from to minutes, which causesthe copper particles to sinter together to form a strong sponge having acontinuous metallic network which is alloyed by an alloy bond to thesupporting back. This copper sponge is then fiuxed by immersion inammonium chloride solution or any other suitable flux disclosed hereinand is subsequently immersed in a bath of molten tin which is preferablymaintained at a temperature of approximately 450 to 500 F., the meltingpoint of tin being 449.4 F. Prior to the immersion of the sponge in theimpregnating bath the aforementioned vacuum is applied and then underevacuated conditions the sponge is immersed and pressure applied for aperiod of immersion approximately from 1 to 2 minutes, which issufficient to cause complete and uniform impregnation of the tin intothe sponge. The tin impregnated copper sponge, if desired, may next becooled to set the impregnated metal although this step is not necessary.The impregnated sponge is then heated under nonoxidizing or reducingconditions to a temperature well above 500 F., for example 1000 to 1900F. for a period up to 10 minutes. During this heating period the tin,which readily dissolves copper, at these higher temperatures uniformlydiffuses into the copper matrix thereby forming a uniform andhomogeneous bronze without destroying the continuity of the matrix. Theperiod of heating, the temperature of the heating step, or both, may bevaried to accomplish partial alloying of the tin.

In a like manner a tin-lead mixture can be used as the impregnatingalloy for a copper matrix in which instance the impregnating bath ismaintained up to fifty degrees above the melting point of the tin leadalloy. In this case, the subsequent heating of the impregnated sponge,which has a uniform dispersion of the lead alloy therethrough, causesthe tin to diffuse into the copper matrix and leave the lead, which isnot readily alloyable with either copper or bronze, in a finely dividedstate within the pores of the bronze matrix.

In a similar manner a bronze sponge can be utilized in which case, asthe tin diffuses therein, the tin content of the bronze, is changed to ahigher percentage than was present in the origi nal sponge.

In place of tin such aforementioned metals as bismuth, cadmium,bismuth-lead or silver-tin etc. can be used as impregnating metals forcopper or bronze sponges, in each case the impregnating temperaturebeing just above the melting point of the impregnating metal or alloyand the subsequent heating step being slightly below the melting pointof the porous metal sponge when a pure metal sponge is used, andpreferably below the melting point of the highest melting constituentmetal when an alloy sponge is used. Likewise, iron sponge can be readilyimpregnated and subsequently alloyed with aluminum and similarly nickelsponge can be transformed into Monel sponge by impregnating with copperetc.

The present method is decidedly advantageous when it is desired toimpregnate and subsequently alloy a sponge with a readily alloyablemetal since such a method as herein described prevents any substantialdissolving action by the impregnating metal on the sponge whereby thestructure of the sponge in its final form is substantially similar tothe structure of the'sponge prior to the tmprtghhtthg thh hhhhthh tttht.

While the embodiment of the present invention as herein disclosed,constitutes a preferred form, it is to be understood that other formsmight be adopted, all coming within the scope of the claims whichfollow.

What is claimed is as follows:

1. The steps in the method of making a metallic structure comprising:providing a porous metal matrix of copper which has intercommunicatingvoids therein by sintering together finely divided non-compacted copperpowder, fiuxing said matrix with a suitable flux so that the fluxpenetrates within the intercommunieating voids of the matrix, immersingthe fiuxed matrix in a molten bath of tin at a temperature only slightlyabove the melting point of tin and for such a short period of time thatthe tin While flowing within the intercommunicating voids of the matrixhas no substantial dissolving action upon the metallic structure of thematrix, removing the impregnated matrix from the bath, and then heatingthe impregnated copper matrix to a temperature well above the meltingpoint of tin whereby the tin difiuses into the copper and simultaneouslyprogressively raises the melting point of the alloy formed by the copperand the tin and thereby prevents the continuity of the resultant matrixfrom being destroyed to form a bronze matrix with intercommunicatingvoids therein.

2. The steps in the method of making a porous metal structure having ametal held within the pores thereof comprising: providing a porous metalmatrix having intercommunicating voids therein by sintering togetherfinely divided noncompacted metal powder, fluxing said matrix with asuitable flux so that the flux penetrates within the intercommunicatingvoids of the matrix, impregnating the matrix with the mixture of metals,one of which readily alloys with the metal of the matrix and the otherof which does not readily alloy with the metal of the matrix byimmersing the porous metal matrix in a molten bath of an alloy of thetwo impregnating metals which bath is maintained at a temperatureslightly above the melting point of said alloy for a short time only andthereby preventing any substantial dissolving action by the readilyalloying impregnating metal upon the matrix, then subsequently heatingthe impregnated metal matrix to a temperature sufiiciently high to causethe readily alloyable metal to uniformly diffuse into the matrix to forman alloy therewith, and leave the remainder of the impregnating metaldispersed within the pores of the metal matrix, and then cooling thealloyed matrix.

3. The steps in the method of making a porous bronze structure havinglead dispersed in the pores thereof comprising: providing a coppermatrix having intercommunicating voids therein by sintering togetherfinely divided non-compacted copper powder, fluxing said matrix with asuitable flux so that the flux penetrates within the interstitial poresof the matrix, impregnating the copper matrix with lead and tin byimmersing the copper matrix in a molten bath of lead and tin for a shorttime only, which bath is maintained at a temperature only slightly abovethe melting point of the lead-tin alloy then subsequently heating theimpregnated metal matrix to a temperature well above the melting pointof the lead-tin alloy and thereby causing the tin to uniformly difiuseinto the copper matrix ant hhht t hthhth thththhh hhththt hthttththt thcontinuous structure of the matrix, and leavin the lead dispersed withinthe interstitial pore of the bronze matrix.

4. The steps in the method of making a metal lic structure comprising:providing a DOIOlJ metal matrix of homogeneous character by sin teringtogether finely divided non-compacte metal powder, fluxing said matrixwith a suit able flux so that the flux penetrates the inter stltialpores of the matrix, impregnating th fluxed porous metal matrix with amixture c metals which includes one metal that is readil alloyable withthe metal in the matrix and. an other metal which is not readilyalloyable wit the metal of the matrix, at a temperature onl slightlyabove the melting point of the impreg nating alloy and for such a timeas to preven any substantial dissolving action by the readil alloyablemetal upon the matrix, then subse quently heating the impregnated porousmete matrix at a temperature well above the impreg nating temperatureand thereby causing th readily alloyable metal to diffuse into the meteof the matrix and form an alloy therewith with out destroying thecontinuous structure of th matrix and leaving the less alloyable metaldis persed within the pores of the matrix.

5. The steps in the method of making a com posite metal structurecomprising: uniforml distributing a loose layer of uncompacted metapowder upon a relatively strong non-porou metal supporting back,subjecting the loose layei in situ upon said back, to such a temperaturean for such a time as will cause the loose metal par ticles tomolecularly bond together and form relatively highly porous matrixhaving inter communicating voids therein and simultaneousl cause saidmatrix to molecularly bond to sai metal back, impregnating the porousmeta matrix with a metal which is readily alloyabl with the metal of thematrix at a tempera ture only slightly above the melting point of thimpregnating metal and for such a time as t prevent the impregnatingmetal from having substantial dissolving effect on said matrix, an thensubsequently heating the impregnate matrix to a temperature sufficientlyhigh to caus substantially uniform difiusion of at least a por tion ofthe impregnating metal into the porou metal matrix and thereby form analloy in sit with the matrix without destroying the con tinuity of thematrix.

6. The steps in the method of making a com posite metal structurecomprising: uniforml; distributing a loose layer of uncompacted metapowder upon a relatively strong non-porous sup porting back, subjectingthe loose layer, in sit upon said back, to such a temperature and fosuch a time as Will cause the loose metal particle to molecularly bondtogether and form a rela tively highly porous matrix having inter-communicating voids therein and simultaneousl; cause said matrix tomolecularly bond to sai metal back, impregnating the porous meta matrixwith a mixture of metals one of whic] readily alloys with the metal ofthe matrix am the other of which does not readily alloy with th metal ofthe matrix at a temperature slightl; above the melting point of themetal mixture am for such a time as to prevent any substantial dissolving action by the readily alloyable impreg nating metal upon thematrix, then subsequentl; heating the impregnating metal matrix to a tem:rature sufficiently high to cause at least a porm of the readilyalloyable metal to uniformly lfuse into the matrix to form an alloythere- 'Lth, and leave the remainder of the impreglted metal dispersedwithin the pores of the etal matrix.

'7. The steps in the method of making a metallic ructure comprising:sintering together finely vided, non-compacted metal powders, to formporous metal matrix, impregnating the matrix formed with a mixture ofmetal including at ast one metal which is readily alloyable with ,emetal of the matrix and' another metal which not readily alloyable withthe metal of the atrix at a temperature only slightly above the meltingpoint of the impregnating alloy and for

